garage/bodyshop phase 's not balanced?

[pbarrett]

was called to a friends business the other day as he lost all power, tells me over the phone they have an isolator open and one of the phases has burnt out at the terminal.

he sad they have lost power several times before

they have an old 100a MEM excel TPN switch fuse straight from the meter to a dis board other side of the unit. 25mm tails

I managed to replace the burnt out tail and contact block and get them operational.

could this have been a simple loose termination or are the phases not balanced correctly.

I did get them to power up everything like it was a busy day so flat out. clamp meter showed a brief 120A load when th booth fans motors kicked in, then a constant70-80A on all phases.

 

[Marvo]

Don't worry about the motor start current. If there's 70-80 Amps on each phase then the balance is fine. It's most likely a poor termination that cause the burned termination or less likely an undersized cable

 

[pbarrett]

cheers marvo, that is what I suspected, I think has caused terminal damage to the rest of the fuse holder on that phase now though, as my friend has text me saying they had a slight power out today, im going to replace the isolator to be on the safe side I think.

 

[Marvo]

Probably not a bad idea if one of the terminals has been badly overheated. Could also be a poor internal switch contact with arcing, would at least be worth checking the volt drop across the switch contacts.

 

[davesparks]

cheers marvo, that is what I suspected, I think has caused terminal damage to the rest of the fuse holder on that phase now though, as my friend has text me saying they had a slight power out today, im going to replace the isolator to be on the safe side I think.

No need to change the whole thing, you can buy the fusebase/switch contact part seperately and just replace the broken bit.
A whole new switchfuse will be a good £300 or so, and be identical internally to the ones installed in the 60's and earlier. MEM haven't changed their patterns in more years than an elephant can remember.

 

[davesparks]

They do get a bit tired over the years if they don't get maintained properly every few years or so.

 

[pbarrett]

I have replaced contact base but cant seem to find a holder base, this looks tired too where it has overheated, which I think now s causing the occasional phase loss the fuse not a nice tight fit

 

[Marvo]

.....causing the occasional phase loss the fuse not a nice tight fit

I'd take that as a sign of irreparable heat damage.

 

[davesparks]

I have replaced contact base but cant seem to find a holder base, this looks tired too where it has overheated, which I think now s causing the occasional phase loss the fuse not a nice tight fit

Get them from MEM, they still make them to the exact same pattern.

 

[davesparks]

I'd take that as a sign of irreparable heat damage.

It's an MEM excel switchfuse, completely modular inside and nothing short of a bomb blast will put it beyond repair, especially the old ones.

 

[Marvo]

It's a manufacturer I'm not familiar with but surely if it's overheated and lost the tension on the fuse holders surely it would need replacing.

 

[davesparks]

Yes, but just the one fuseholder, not the whole thing.

Each fuseholder base is a completely seperate porcelain unit screwed into the metal box. The switch contact blocks are seperate porcelain items and so is the neutral terminal.
There is a seperate set of moving contacts shaped like big staples which are mounted on a removable insulating bar.
The actual fuseholder is also a seperately available item.

It is an ancient design which they haven't changed for many many years.
To upgrade a 100A switchfuse with rewire able fuses you just purchase the current 100A hmrc fuse holder and plug it straight in to the existing base.

The only thing that has really changed is the colour they paint the box and the terminal screws now have pozi heads instead of slotted.

 

[Marvo]

Sounds like quite a thing. Most of the fuse holders and isolators we deal with in the 100A or less category are just disposable, if there's anything hinkey about them we just fit a new item.

 

[davesparks]

I'll start the laptop up and see if I can get a decent picture up.

 

[Lucien Nunes]

Bog standard over here. MEM were one of the biggest and best in the UK at what they did, around since the year dot although they are now part of Eaton. The Exel has been one of their standard lines ever since they moved from cast iron to pressed steel. In the UK they are still the metalclad isolator / switchfuse of choice for heavy duty from 20-100A. The Glasgow series takes the range upwards from 100A. If I need a decent metalclad isolator / SF, I don't have to think too hard about which to use. If I need parts, I go and raid one of the many dozen used units I have in the stores.

 

[davesparks]

Here we go, i've found a few pics from a job I did a while ago:

Firstly an old one on its way out of the installation, its a single phase + switched neutral version, the three phase is a bit wider with three of the fuseholder units in a row and a separate unswitched neutral block with a screwed disconnect link.
The jobby to the left of it is a three phase changeover/motor reversing switch by the same maker and using the same switch contacts and moving contact bar.
And the big blue things are old stage lighting dimmers (4 x rheostat in a box, each rated at 1000W I think)







And a pic of a very old one and the top half of a new coloured one,

 

[Engineer54]

One of the few decent bits of electrical kit that is still fully component serviceable, in what is now a throw away society.

 

[davesparks]

Unfortunately they seem to be starting to make the terminal screw out of cheese though like everything else. And putting this damned pozi/slotted hybrid screws in them.

I don't understand why they didn't just stick with the strong slotted ones they've been using since the dinosaurs left the planet.

 

[Engineer54]

Unfortunately they seem to be starting to make the terminal screw out of cheese though like everything else. And putting this damned pozi/slotted hybrid screws in them.

I don't understand why they didn't just stick with the strong slotted ones they've been using since the dinosaurs left the planet.

Why, ....because like many people here, they ''think'' that New is always better, that and any excuse to cut material costs!! However, we oldies ''KNOW'' better!!